Strålman's elite possession stats actually come from shot suppression, not shot generation, which is surprising considering that he is a small, skilled defenceman. A good breakout is likely part of that, i.e. not getting hemmed in your own zone, but I think a big part of his game is neutral zone D. He is likely good at forcing dump-ins and breaking up plays before they even reach the Rangers' zone, while a guy like Girardi likely allows a ton of carry-in's (his breakouts are usually terrible as well though). Looking deep into the numbers Strålman and Girardi generate about as many shot attempts for vs expectation (slight edge to Strålman, both players are positive) but Strålman blows Girardi out of the water in shot attempt suppression vs expectation.

The problem is in the way their partners tend to play the game combined with their own strengths. McDonagh and Staal are very similar players, stylistically, in the defensive zone and defending the rush. A lot of pucks get freed up by both of them. Stralman is better at the breakout than Girardi is. It's why Stralman's advanced stats help every pair he's on compared to Girardi's. It's not because he's a better defensive player, but because his skills are a better compliment to the other defensemen he plays with.

Look at it from the other direction too. Girardi plays a very similar game to Staal, like McDonagh does. One of the biggest reasons we saw McDonagh take a step forward offensively this year is because he started taking better advantage of the pucks Girardi frees up (there are other reasons too). In other words, he adjusted his game to be more like Stralman's, but he's even better at it. If McDonagh could adjust just a little further in that direction, then it could really launch him into a Norris contender.